The Effect of Oxygen Depletion on Anaerobic Organic Matter Degradation in Marine Sediments

Abstract

The effect of oxygen depletion in bottom waters on anaerobic microbial activity was studied in a marine sediment with phytoplanktonic detritus as the main organic matter source. Sulphate reduction rates, sediment metabolism, pore water pools of inorganic and organic carbon compounds and ammonium and particulate pools (organic matter and chlorophyll-a) were examined in intact sediment cores exposed to a simulated oxygen depletion event. Sulphate reduction was stimulated shortly (2 days) and attained rates that were up to 8 times higher. After the initial stimulation, sulphate reduction rates decreased to a level similar to oxic conditions, and the longer term effect (2 weeks) of oxygen depletion on sulphate reduction was minor. Chlorophyllaprofiles and closed anoxic incubations showed that the organic matter in the surface layer was easy to degrade and sulphate reduction accounted for approximately half of the carbon oxidation in the field cores. The pore water concentrations of dissolved organic carbon (DOC) were high in the anoxic cores indicating a slower anaerobic mineralization of dissolved organic matter. The potential effects of enhanced pore water DOC during oxygen depletion events are discussed.